1. Field of the Invention
This invention relates to an improved method and composition for counteracting and/or inhibiting shrinkage in cementitious systems during setting.
The term "cementitious systems", as used herein, is intended to include compositions which generally possess the characteristic of hardening under water and includes, for example, settable hydraulic cement, hydraulic lime, gypsum and like materials, as well as mixtures of the foregoing with aggregates and water such as concrete, mortar, grout and products made therefrom.
The terms "shrinkage inhibition" and "shrinkage counteraction" are used essentially interchangeably herein to describe, as a minimum, a reduction in the shrinkage of cementtitious systems and/or, advantageously, achieving a volume equal to or greater than the system placement volume, and encompass similar terms such as "shrinkage compensation" and "shrinkage elimination". The term "setting" is used broadly herein to generally describe the state of the cementitious system prior to the hardened state and encompass the plastic state.
2. Description of the Prior Art
Methods and means for inhibiting shrinkage of hydraulic cement mixtures during setting and hardening have previously been suggested. The prior art methods have included the addition, to such mixtures, of various expansion agents, such as aluminum powder and iron filings, which are generally added at the mixing during the preparation of the cement mixture. These procedures have been impractical because of, among other reasons, lack of adequate control of expansion. It has also been found that certain unique materials can eliminate shrinkage in concrete due, it is theorized, to the release of entrapped gas from porous particulate materials upon adsorption of water from the cementitious system. Materials such as fluid coke, a combination of fluid coke and delayed coke, which are by-products of the petroleum industry, and porous particulate materials, such as so called industrial adsorbents, have been used with various types of cementitious mixtures to successfully inhibit shrinkage. See for example U.S. Pat. No. Re.26,597; U.S. Pat. Nos. 3,503,767; 3,519,449; 3,794,504; and 3,890,157.
The successful utilization of certain materials as shrinkage inhibitors in cementitious systems is unpredictable. For example, fluid coke is a carbonaceous material and therefore its success as a shrinkae inhibitor without having deleterious effects on the cementitious system is surprising. Thus, U.S. Pat. No. Re. 26,597 compares the effects of fluid coke, delayed coke and carbon black on grout shrinkage and concludes therefrom that no other type, i.e., other than fluid coke, of coke or carbon has the effect of expanding cement in a controlled matter. The patent also notes that coal clinkers may cause expansion but in a harmful and an uncontrolled amount with the expansion being related to the clinker sulfur content. While clinker and coke breeze have been added to cementitious systems as aggregates, "Concrete Technology", Vol. 1, John Wiley & Sons, New York, 1962, pp. 146-7, points out that the combustible matter, chiefly carbon, in these materials has lead to failures due to excessive expansion when they have been used as a concrete aggregate. The expanion may be exceptional and is apparently uncontrollable due to moisture movement on wetting which can result in shrinkage on drying.
U.S. Pat. No. 3,503,767 states that the amount of fluid coke required to eliminate shrinkage can be reduced if the particle size is fine. U.S. Pat. No. 3,519,449 finds that the amount can be reduced if the moisture content of the fluid coke is controlled and discloses drying the fluid coke to drive out substantially all the moisture. U.S. Pat. No. 3.890,157 discloses that an adsorbent-like porous particulate solid material, such as activated carbon, having entrapped gas within its pores and capable of adsorbing water and discharging the gas during cementitious system setting and hardening, counteracts shrinkage.
Carbonaceous materials have been added to cement compositions for very limited specific purposes in the oil well cementing environment. Thus, U.S. Pat. No. 2,609,882 discloses adding activated carbon to a cement composition for cementing oil wells in order to offset the deleterious effects, on the cement, of the oil well drilling mud additives. U.S. Pat. No. 3,376,146 discloses the addition of large amounts, at least 20 percent by weight or more, of carbon including ground lignite coal, bituminous coal, anthracite coal, graphite, petroleum coke and coke to a cement composition for cementing oil wells in order to provide a low density composition. Neither of the aforementioned patents dealing with oil well cementing recognizes any advantage or disadvantage of the added carbon material other than that described. For general application it is still believed that the addition of carbon such as coal and lignite is detrimental to concrete. See, for example, "Concrete Construction Handbook", Joseph J. Waddell, McGraw Hill, 2nd Ed., pp. 236-237 pointing out the limits for deleterious substances in fine and coarse aggregates for concrete and identifying coal and lignite as deleterious additives. The ACI (American Concrete Institute) suggests that aggregates meet ASTM Specification C33 which limits the maximum weight percent of coal or lignite to 1 percent or less in sand, for aggregate, when tested according to ASTM C123. According to ASTM C330-69, lightweight aggregates for structural concrete should not contain deleterious organic impurities.